Digital Sequencing with Analog Devices

Simplified Power Sequencing (XAPP1375)

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The LTC2977 from Analog Devices is a feature-rich power management IC that is capable of sequencing, margining, trimming, supervising output voltage for OV/UV conditions, providing fault management, and accurate voltage readback for up to eight DC/DC converters. The LTC2977 provides comprehensive supervision, control, and recovery modes that are conducive to any application where safety is of concern. The supervisor functionality allows for control of the VRMs output voltage through the eight channel VOUT_EN outputs and can monitor up to eight of these rails while allowing for expansion with additional devices. Many of the functions, controls, and supervision are handled directly by the standardized command power management bus (PMBus) protocol used to communicate with this device. When used in the closed loop servo mode, it can margin or trim supplies within 0.25% of target and can be powered from 3.3V, or 4.5V to 15V.

The designer can control the power sequence, transfer voltage, current, and temperature data across the PMBus to the controller, as well as transfer faults and write to the LTC2977 internal EEPROM using the PMBus interface. There are dedicated pins for alert, fault, and PG signals for system level coordination. There is a recovery mode as a response to a fault. Another advantage to using a digital sequencer is the ability to configure settings and store fault logs in EEPROM.

Figure 1. Simplified Diagram for Channel Sequencing, Trim, Margin, and Supervision

For a full selection of power sequencers from Analog Devices, see Analog Devices.